Generators are used to generate a majority of the power on current electric power grids. These generators, which can be synchronous generators or permanent magnet generators, for example, are used to convert mechanical energy from internal combustion, wind, nuclear, and hydraulic sources, for example, into electrical energy. Modern generators can produce hundreds of megawatts each.
Modern wound-rotor generators include a rotor and a stator, each with one or more electrical windings. A magnetic field on the rotating rotor is generated by a current passing through the rotor winding, which induces an electrical current in the stator winding(s) and creates alternating current (AC) electricity. An output voltage of the generator can be controlled by controlling the current flow in the rotor winding (and therefore the strength of the magnetic field, which induces a voltage on the stator winding(s)). In some cases, the current flow in the rotor winding may be supplied by a direct electrical connection to the generator controller using, e.g., slip rings. In other cases, the current flow may be controlled from the generator controller using an armature winding to the rotor through electromagnetic induction. One or more loads can be connected to, and powered by, the output of the stator. In some embodiments, the output of the stator can be rectified to produce direct current (DC) electricity.
During a load fault condition, such as a short-circuit fault occurring in the load, the electrical energy delivered by the electrical generator to the load should be limited to reduce a severity of consequences of the fault. However, even though the generator controller can turn off the exciter current, the rotor magnetic field will not immediately fall to zero due to the stored magnetic energy in the main field windings and a relatively large time constant. This condition results in the field current “free-wheeling” through the components of the rotor which, in turn, causes the main armature to continue producing current. Unfortunately, this current is being provided to a short-circuit, compounding the problem. This makes it difficult to clear the load fault (i.e., because it is still energized) and can overheat both the rotor and the stator. If this condition persists long enough, there is a risk of permanent damage to the load, the distribution system, and/or the generator. To address these and other issues, the present disclosure is submitted.